Default create_schematic to A3 paper size with configurable parameter

A4 is too small for real schematics. A3 matches US engineering
convention (close to ANSI B/Tabloid) and is KiCad's standard
template size. Batch JSON also supports paper_size field.

src/mckicad/tools/batch.py

@@ -363,6 +363,14 @@ def _apply_batch_operations(
     collisions_resolved = 0
     wire_collisions_resolved = 0
 
+    # 0. Paper size (if specified in batch)
+    batch_paper = data.get("paper_size")
+    if batch_paper:
+        try:
+            sch.set_paper_size(batch_paper)
+        except Exception:
+            logger.warning("Could not set paper_size to '%s'", batch_paper)
+
     # 1. Components (multi-unit supported natively by kicad-sch-api)
     for comp in data.get("components", []):
         ref = comp.get("reference")

src/mckicad/tools/schematic.py

@@ -104,8 +104,15 @@ def _expand(path: str) -> str:
 # ---------------------------------------------------------------------------
 
 
+_VALID_PAPER_SIZES = {"A4", "A3", "A2", "A1", "A0", "Letter", "Legal", "Tabloid"}
+
+
 @mcp.tool()
-def create_schematic(name: str, output_path: str) -> dict[str, Any]:
+def create_schematic(
+    name: str,
+    output_path: str,
+    paper_size: str = "A3",
+) -> dict[str, Any]:
     """Create a new, empty KiCad schematic file.
 
     Generates a valid .kicad_sch file at the specified location that can be
@@ -115,9 +122,12 @@ def create_schematic(name: str, output_path: str) -> dict[str, Any]:
         name: Human-readable name for the schematic (e.g. "Power Supply").
         output_path: Destination file path. Must end with .kicad_sch.
               Parent directory will be created if it does not exist.
+        paper_size: Paper size for the schematic sheet. Default "A3".
+              Valid sizes: A4, A3, A2, A1, A0, Letter, Legal, Tabloid.
+              US schematics typically use A3 or Tabloid (ANSI B, 11x17").
 
     Returns:
-        Dictionary with ``success``, ``path``, and ``engine`` keys.
+        Dictionary with ``success``, ``path``, ``paper_size``, and ``engine`` keys.
     """
     err = _require_sch_api()
     if err:
@@ -131,19 +141,30 @@ def create_schematic(name: str, output_path: str) -> dict[str, Any]:
             "error": f"output_path must end with .kicad_sch, got: {output_path}",
         }
 
+    if paper_size not in _VALID_PAPER_SIZES:
+        return {
+            "success": False,
+            "error": (
+                f"Invalid paper_size '{paper_size}'. "
+                f"Valid sizes: {', '.join(sorted(_VALID_PAPER_SIZES))}"
+            ),
+        }
+
     try:
         parent = os.path.dirname(output_path)
         if parent:
             os.makedirs(parent, exist_ok=True)
 
         sch = _ksa_create(name)
+        sch.set_paper_size(paper_size)
         sch.save(output_path)
 
-        logger.info("Created schematic '%s' at %s", name, output_path)
+        logger.info("Created schematic '%s' (%s) at %s", name, paper_size, output_path)
         return {
             "success": True,
             "path": output_path,
             "name": name,
+            "paper_size": paper_size,
             "engine": _get_schematic_engine(),
         }
     except Exception as e: